Sometimes, expensive gears cannot guarantee it will work well with other equipments and also in the room.

The receiver will act as the control unit only.
In an integrated amp/receiver, it is consisted of two parts.
One is the control (something like pre amplifier) and the other is the power amplifier.

If you are adding power amp to your receiver, the power amp will take over the job from receiver to drive the speakers but the signals are being fed by the receiver's pre amplifier part.

Power amp can maintain a more consistent output compared to receiver's built in power amp. The drop in performance is due to distortions and heat.
(Sorry if explanation not clear... but something like that lar.. )

Speakers have higher chances of being damaged by low powered amps rather than high powered amps.

Not really. Surely can feel the differences.
If you have poweramp, the AVR's output is already nothing (useless).
Coz the poweramp will drive the speakers.
AVR will be the signals processor only.

Poweramp usually have a better output consistency.
Very useful if your speakers are demanding and also high volume listening.
So, with a poweramp, the performance will surely increase.

I might have no idea in mutlichannel HT systems but when I looked at the Emotiva, I feel that the prices are very reasonable given that sort of performance.
Hence, the Emotiva is the focus of our fellow forummers here.

Not to say that other brands are not good.
There are lots of brands that are good but most of them dont come cheap.